Rotating turbomachinery such as, for example, gas turbine engines and auxiliary power units (APU) utilize speed sensors to detect the rotor speed. Rotor speed is monitored for performance and safety reasons. The engine controller may, for example, adjust the fuel flow to maintain a prescribed speed for any load driven by the engine. Typically at least two speed sensors are used for reliability and for safety.
If the speed sensor readings diverge, the controller may control to the higher speed reading. If both speed sensor readings become erratic, the controller may shut the engine off. For example, the controller may deduce that it cannot control the engine speed in response to an erratic reading. In some instances, erratic readings may result from engine vibrations physically shifting the speed sensors. As a result of shifts, the values read by the speed sensors may fluctuate between high speeds and low speeds at a more rapid rate than the monitored engine can possibly accelerate or decelerate or the two speed readings may diverge and converge to indicate engine vibration. Engine vibration may be caused by various sources.
Engine health in gas turbine engines may be monitored for safety reasons and to perform maintenance as needed. One sign of engine health may be the vibration signature of the engine. When the vibration level exceed a certain level, it may be desirable to shut off the engine or to schedule a maintenance action. However, vibration monitoring equipment may be cumbersome and expensive. Furthermore, many engines do not carry additional health monitoring system.